code: def test_unique(self, ordered):
      # GH38140
      dtype = CategoricalDtype(["a", "b", "c"], ordered=ordered)
  
      # categories are reordered based on value when ordered=False
      cat = Categorical(["a", "b", "c"], dtype=dtype)
      res = cat.unique()
      tm.assert_categorical_equal(res, cat)
  
      cat = Categorical(["a", "b", "a", "a"], dtype=dtype)
      res = cat.unique()
      tm.assert_categorical_equal(
          res, Categorical(["a", "b"], dtype=dtype)
      )
  
      cat = Categorical(["c", "a", "b", "a", "a"], dtype=dtype)
      res = cat.unique()
      exp_cat = Categorical(["c", "a", "b"], dtype=dtype)
      tm.assert_categorical_equal(res, exp_cat)
  
      # nan must be removed
      cat = Categorical(["b", np.nan, "b", np.nan, "a"], dtype=dtype)
      res = cat.unique()
      exp_cat = Categorical(["b", np.nan, "a"], dtype=dtype)
      tm.assert_categorical_equal(res, exp_cat)
  
imports: import re
  import sys
  import numpy
  import pytest
  from pandas.compat import PYPY
  from pandas import Categorical, CategoricalDtype, DataFrame, Index, NaT, Series, date_range
  import pandas._testing
  from pandas.api.types import is_scalar
label_desc: Use image node_id 13 for calling the TestCategoricalAnalytics obj's underlying member method code with example usage: obj.test_unique(ordered) without return types